The overall objective of this grant is to investigate the structure and function of viral and cellular mos proteins. Our previously published studies have provided convincing evidence that the viral mos protein is a serine/threonine protein kinase. Furthermore, our studies with various mutants of the viral mos gene have shown an absolute correlation between the cellular transformation function of the activated oncogene and its associated protein kinase function. This correlation indicates that the serine/threonine kinase function of v-mos proteins plays an essential role in malignant transformation induced by Moloney mouse sarcoma virus. We proposed to investigate how the p37env-mos protein kinase activity is regulated via phosphorylation and how it relates to cell cycle regulation. We have identified the c-mos gene product (p43c-mos) in germ cells from mouse testes. Western blotting experiments have detected a similar size c- mos protein in somatic cells. Further studies are underway on the struc- ture and function of this protein, and to determine whether it may be functionally associated with components of the maturation promotion complex (MPF). The specific aims include: 1) Characterize the components of two complexes (500-kDa and 98 kDa) that house p37 env-mos in chronically transformed cells; 2) Characterize the interaction of p37env-mos with p34cdc2 protein kinase (a component of MPF) detected in 500-kDa size complexes from chronically transformed (MoMuSV 3T3 cells; 3) Determine whether p37env-mos and p43c-mos phosphorylate cyclin (a component of MPF), and other mitotic proteins; 4) Study the cell cycle regulation of the p37env-mos kinase by phosphorylation; 5) Investigate the role of protein kinase C and other cellular kinases including p34cdc2 of MPF in the activation of p37env-mos kinase; 6) Search for important substrates for p37env-mos kinase; 7) Determine the biochemical basis of vimentin altera- tion by p37env-mos; 8) Characterize the testicular and somatic cell forms of p43c-mos; 9) Determine the cell cycle regulation of somatic p43c-mos and its possible association with components of MPF; 10) Clone the v-mos and c- mos genes in a baculovirus vector, which will allow the production of higher amounts of active mos proteins for further biochemical studies.